A parallel optical communications module is a module having multiple transmit (TX) channels, multiple receive (RX) channels, or both. A parallel optical transceiver module is an optical communications module that has multiple TX channels and multiple RX channels in the TX and RX portions, respectively, of the transceiver. A parallel optical transmitter module is an optical communications module that has multiple TX channels, but no RX channels. A parallel optical receiver module is an optical communications module that has multiple RX channels, but no TX channels.
The TX portion of a parallel optical communications module comprises components for generating modulated optical signals, which are then transmitted over multiple optical fibers. The TX portion includes a laser driver circuit and a plurality of laser diodes. The laser driver circuit outputs electrical signals to the laser diodes to modulate them. When the laser diodes are modulated, they output optical signals that have power levels corresponding to logic 1s and logic 0s. An optics system of the transceiver module focuses the optical signals produced by the laser diodes into the ends of respective transmit optical fibers held within a connector that mates with the transceiver module.
The RX portion of a parallel optical communications module includes a plurality of receive photodiodes that receive incoming optical signals output from the ends of respective receive optical fibers held in the connector. The optics system of the transceiver module focuses the light that is output from the ends of the receive optical fibers onto the respective receive photodiodes. The receive photodiodes convert the incoming optical signals into electrical analog signals. An electrical detection circuit, such as a transimpedance amplifier (TIA), receives the electrical signals produced by the receive photodiodes and outputs corresponding amplified electrical signals, which are processed in the RX portion to recover the data.
A mid-plane mounting configuration for a parallel optical communications module is one in which the module is mounted on the surface of a host printed circuit board (PCB). A typical mid-plane mounting configuration includes a socket that is mounted on the host PCB and a parallel optical communications module that is mounted in the socket. The socket has a bottom and typically has side walls. Arrays of electrical contacts are disposed on upper and lower surfaces of the bottom of the socket. The parallel optical communications module has an array of electrical contacts disposed on its lower surface that electrically connects with the array of electrical contacts disposed on the upper surface of the socket when the module is mounted on the socket. A well known type of socket that is used for this purpose is a mezzanine-type socket, which is a molded plastic receptacle having an array of electrically-conductive balls, known as a ball grid array (BGA), disposed on its lower surface, and having an array of electrically-conductive spring fingers disposed on its upper surface. Other types of sockets have similar designs. Some sockets have a land grid array (LGA) instead of a BGA on their lower and/or upper surfaces.
The socket is typically secured to the surface of the host PCB by drilling holes through the host PCB and inserting fastening devices (e.g., screws) through the holes formed in the host PCB and through holes formed in the socket to fasten the socket to the host PCB. After the socket has been secured to the host PCB, the optical communications module is mounted on the socket such that the array of electrical contacts disposed on the lower surface of the module is electrically connected to the array of electrical contacts disposed on the upper surface of the bottom of the socket. Securing the socket to the host PCB in this manner reduces mechanical shocks and vibrations to the module that could otherwise damage the module or detrimentally affect its performance due to loss of connectivity between socket and module.
One of the problems associated with securing the socket to the host PCB in this manner is that electrical conductors of the host PCB cannot be routed through the locations where the holes have been drilled in the host PCB. This presents challenges when it comes to designing the routes of the host PCB. Another problem that is caused by drilling holes in the host PCB is that the processes of drilling the holes and using fastening devices to secure the socket to the host PCB are manual processes that are very time consuming and not well suited for automation.
Accordingly, a need exists for a method and apparatus for mid-plane mounting a parallel optical communications module on a host PCB that eliminate the need to drill holes in the host PCB and that allow the module to be secured to the host PCB without having to manually install fastening devices.